Method for determining an absolute rotational position of a vehicle steering column

Abstract

A method for determining an absolute rotational position of a vehicle steering column is provided. In one exemplary embodiment, the method determines a relative position of a steering assist motor utilizing a relative position sensor. Thereafter, the method determines the absolute rotational position of the vehicle steering column based upon the relative position of the steering assist motor.

1. A method for determining an absolute rotational position range of a vehicle steering column, comprising:
 initializing an initial absolute rotational position value equal to a predetermined value; 
 rotating the vehicle steering column in a first rotational direction; 
 determining a plurality of absolute rotational position values indicating a plurality of absolute rotational positions of the vehicle steering column during the rotation of the vehicle steering column; and 
 determining the absolute rotational position range of the vehicle steering column based on the plurality of absolute rotational position values, and both an upper rotational position limit value and a lower rotational position limit value associated with the vehicle steering column; 
 wherein said determining a plurality of absolute rotational position values comprises determining an absolute rotational position value at each of a plurality of absolute rotational positions of the vehicle steering column, the plurality of absolute rotational positions being encountered during the step of rotating the vehicle steering column in the first rotational direction. 
 
     
     
       2. The method of  claim 1 , including:
 detecting vehicle ignition shutdown; and 
 iteratively determining a plurality of ignition shutdown absolute position values associated with the vehicle steering column for a predetermined time interval after the vehicle ignition shutdown; and comparing said plurality of absolute rotational position values with said plurality of ignition shutdown absolute rotational position values to determine a last valid absolute rotational position value. 
 
     
     
       3. The method of  claim 2 , including storing said last valid absolute rotational position value in a non-volatile memory device. 
     
     
       4. The method of  claim 1 , including storing a last valid absolute rotational position value from the plurality of absolute position values, in a non-volatile memory device. 
     
     
       5. The method of  claim 1 , wherein the predetermined value comprises a rotational position value stored in a memory device during a prior ignition cycle. 
     
     
       6. The method of  claim 1 , further comprising determining whether a valid absolute rotational position value was stored in a memory device during a prior ignition cycle. 
     
     
       7. The method of  claim 6 , further comprising setting a current absolute rotational position value equal to the valid absolute rotational position value stored in the memory device during the prior ignition cycle. 
     
     
       8. The method of  claim 7 , further comprising executing an autocentering subroutine comprising:
 receiving a first signal from a column torque sensor operably coupled to the steering column; 
 determining a column torque value based on the first signal; and 
 summing the column torque value with a commanded torque value to determine a pinion torque value. 
 
     
     
       9. The method of  claim 8 , further comprising receiving a second signal from a motor position sensor operably coupled to a steering assist motor and iteratively determining a motor velocity value based on the second signal. 
     
     
       10. The method of  claim 9 , further comprising receiving a third signal from a vehicle speed sensor and iteratively determining a vehicle speed value from the third signal. 
     
     
       11. The method of  claim 8 , further comprising determining whether the autocentering subroutine was previously used for determining an absolute rotational position of the steering column. 
     
     
       12. The method of  claim 11 , further comprising determining an absolute an absolute rotational position of the steering column using a travel exclusion subroutine. 
     
     
       13. The method of  claim 12 , wherein the travel exclusion subroutine comprises:
 calculating a current relative rotational position value based on signals from a relative position sensor operably coupled to the steering assist motor; 
 initializing a maximum absolute starting position value based on a maximum expected travel of the steering system; 
 initializing a minimum absolute starting position value based on a minimum expected travel of the steering system; 
 calculating a maximum absolute starting position value based on a difference between the current relative rotational position value and the maximum expected travel of the steering system; 
 calculating a minimum absolute starting position value based on a difference between the current relative rotational position value and the maximum expected travel of the steering system; 
 calculating a total maximum absolute starting position value based on the maximum absolute starting position value; 
 calculating a total minimum absolute starting position value based on the minimum absolute starting position value; 
 determining an absolute position range value based on the total maximum absolute starting position value and the total minimum absolute starting position value; 
 calculating a maximum absolute current position value based on a sum of the current relative rotational position value and the total maximum absolute starting position value; 
 calculating a minimum absolute current position value based on a sum of the current relative rotational position value and the total minimum absolute starting position value; and 
 setting the current absolute rotational position value equal to the minimum absolute current position value. 
 
     
     
       14. The method of  claim 13 , further comprising determining whether the maximum absolute current position value is less than zero. 
     
     
       15. The method of  claim 13 , further comprising determining whether the minimum absolute current position value is greater than zero. 
     
     
       16. The method of  claim 7 , further comprising retrieving an absolute rotational position range determined by a travel exclusion subroutine. 
     
     
       17. A method for storing an absolute rotational position value associated with a vehicle steering column, comprising:
 detecting vehicle ignition shutdown; 
 iteratively determining a plurality of absolute rotational position values associated with the vehicle steering column for a predetermined time interval after the vehicle ignition shutdown; and 
 storing a last valid absolute rotational position value from the plurality of absolute rotational position values, in a non-volatile memory device; 
 wherein said determining a plurality of absolute rotational position values comprises determining an absolute rotational position value at each of a plurality of absolute rotational positions of the vehicle steering column, the plurality of absolute rotational positions being encountered during a step of rotating the vehicle steering column.